This is a good refresher for an experienced Lisp programmer,
as well as being an excellent second text for the beginner. (I think
it's a bit too terse to use as a first text for a beginner, but you
may want to look at it and see whether you think it's approachable.)

Dubbed "CLtL2," this was an interim interpretation of the work of the ANSI
standardization committee. It has no standing as part of the standards
process, but was used by many Lisp vendors to anticipate the final
outcome of the committee's work. Some Lisp systems still implement
portions of both the CLtL2 description and the ANSI standard.

Slade's book is probably the best book available on actually
using a Common Lisp environment for something other than AI
programming. I think it's suitable for a beginner, but should
probably be supplemented by another title that provides better
insight into the Lisp language.

When I was first learning Common Lisp, I found Wilensky's
book the most helpful at exposing some of Lisp's unique concepts,
such as closures. This book is easy to read (without being
patronizing) and includes a lot of very clear examples. There's also
a brief Common Lisp reference in the appendix. I still recommend
this as a first book for beginners.